A fuel cell stack that includes at least one electricity generator generating electric energy through an electrochemical reaction between hydrogen and oxygen and a cooling system are provided. The electricity generator includes a membrane-electrode assembly, separators on both sides of the membrane-electrode assembly, and cooling channels placed approximately parallel to a first direction of the membrane-electrode assembly, where a coolant flows through the cooling channels, and where the cooling channels have different distribution densities in a direction perpendicular to the first direction of the membrane-electrode assembly.